Conventional weaving reeds, rotors and functional equivalents having fixed dent spacing produce finished fabrics with variable warp end density across the entire width of the fabric excluding any possible special selvedge. Most fabrics have different variations in warp end density across the width of finished fabrics due to different yarns and processes. In the case of air bag fabrics, there may be less or more warp end density towards the fabric's edge. In the case of lesser density toward the fabric edge, this is caused by the weaving and finishing processes in which the fabric's edges will be stretched out more than the middle part of the fabric due to tension and heat. As a result of these factors, the density of the finished fabric varies across its width and, consequently, the center of the fabric is more dense. This difference in density can be viewed by studying the finished fabric. Such a finished fabric has a density curve, that is, warp end density as measured in ends/inch, with an inverted U shape as depicted in FIG. 2, where a greater density exists at the center of the finished fabric. The actual warp end density varies across the width of the fabric from the left (L), through the left center (LC), center (C), right center (RC), and to the right (R) portions of the fabric. Some fabrics, in particular, certain of those produced for paper making processes, are subject to different processing conditions which result in a density curve opposite to that of the typical fabric previously discussed. Typically, the edges of these finished paper making fabrics are more dense than the middle.
This variation in warp end density across the entire width of a fabric will affect the mechanical properties of the fabric, especially the air permeability. Air permeability is a function of fabric density (i.e. the denser the fabric, the lesser the air permeability). The fabric density is controlled by warp end density and filling yarn (weft yarn) density for chosen yarns, weave, loom, finishing processes and other weaving conditions. For instance, a typical air bag fabric produced with a conventional reed, which is either plain or profiled, may produce a fabric with a warp end density variation across the width of the fabric as depicted in FIG. 2. There is virtually no filling yarn density variation under normal conditions. Therefore, the density variation across the width of a given fabric is caused by the variation of warp end density.
A typical prior art reed 2 is shown in FIGS. 1, 1A, where a plurality of reed wires 4 are connected at their ends to a top baulk 6 and a bottom baulk 8. The reed wires 4 are separated by spaces 10. A dent 12 comprises a wire 4 and an adjacent space 10. A conventional reed wire 4 is shown in FIG. 1B, while a profile reed wire 4' is shown in FIG. 1C.
Air permeability is a critical property of some industrial fabrics such as air bag and filtration fabrics. In the case of air bag fabrics, manufacturers have used many methods to control air permeability including the use of calendering, coatings, impregnation, special weave designs, special air bag constructions, envelopes and layers of differing air permeability, and other methods. These methods may result in: increased costs, limited recyclability in the case of coatings, increased waste, and complicated constructions. The venting of air bags through the fabric may not be possible due to variation in air permeability of the fabric and the resulting unpredictable mode of operation. An example of an air bag with vent holes is shown in U.S. Pat. No. 5,566,972 to Yoshida et al. Examples of air bags using several fabric sections with differing air permeability are seen in U.S. Pat. No. 5,375,878 to N. Ellerbrook, and U.S. Pat. No. 5,566,434 to A. W. Beasley. Another method for making air bag fabric is to utilize special yarns to weave a fabric of low air permeability obviating the need for coating or other processes, as seen in U.S. Pat. No. 5,474,836 to Nishimura et al., and U.S. Pat. No. 5,508,073 to Krummheuer et al. The present invention can improve such a fabric by providing virtually no variation of air permeability across the width of the fabric and may possibly reduce fabric waste in the process of making an air bag. The present invention can also offer an air bag fabric of variable density, which, after construction into an air bag, could result in more uniform air permeability at maximum deployment.
A non-uniform product may result, such as in the case of paper making fabrics, from variations in the fabric. Examples of paper making fabric are shown in U.S. Pat. No. 4,649,964 to R. W. Smith and U.S. Pat. No. 4,588,632 to Gisbourne et al. The present invention can provide a uniform fabric.
A fabric having a differential density is depicted in U.S. Pat. No. 4,698,276 to Duval et al., which is an example of a decorative fabric used to produce drapery. The present invention can produce a fabric which may be suitable for this usage while obviating the need for a complicated construction provided by the assemblage of strips of fabric with various fabric densities. Further, a fabric of variable densities may be suitable for an air bag fabric whereby these densities, when predetermined, could produce a controlled deflation of the air bag by, for example, utilizing a greater density where the fabric stretches more and a lesser density where the fabric stretches less to produce, in effect, less or possibly no variation in air permeability.
Reed type devices which do not perform strenuous beat-up functions are shown, for example, in U.S. Pat. No. 5,368,076 to F. H. Curzio. This reed is actually a warp guiding device but is designed to affect warp end density in net type, loosely woven type fabrics. These fabrics are intended to act as reinforced fabric for composite materials to cover three dimensional mandrels. This reed is of a different design peculiar to making net fabrics where consistent air permeability is not a factor. The reed is shaped to make fabrics for a three dimensional mandrel. Further, this reed design could not perform the functions of the present invention.
Other reed designs include reeds with adjustable or removable dents such as those depicted in U.S. Pat. No. 5,029,617 to Anderson et al. The reed of Anderson cannot correct the warp end density variation as can the present invention because of the spaced relationship of the dents. Regardless of how closely spaced the dents are made in the removable dent reed it could not offer the control of warp end variation available in the present invention. Each adjacent reed wire and removal of same in this removable dent reed would preclude providing the desired spacing needed to produce the fabrics thereby produced by the present invention. Reeds with adjustable or removable dents are utilized generally to insert a larger warp yarn, perhaps to effect a change in the appearance of a decorative fabric, provide a certain selvedge, or provide reinforcement in an industrial fabric. Further, these reeds are also employed to ease maintenance, as a damaged wire can be readily replaced. The adjustable reed may, for instance, be used to produce net shaped fabrics in a variety of shapes, as seen in U.S. Pat. No. 5,465,762 to G. L. Farley. Another type of reed is depicted in U.S. Pat. No. 5,158,116 to Kazuo et al., whereby the dent spacing varies to accommodate thick yarns to facilitate the weaving process.